by Traci Watson, Special for USA TODAY

by Traci Watson, Special for USA TODAY

The vast glaciers of western Antarctica are rapidly melting and losing ice to the sea and almost certainly have "passed the point of no return," according to new work by two separate teams of scientists.

The likely result: a rise in global sea levels of 4 feet or more in the coming centuries, says research made public Monday by scientists at the University of Washington, the University of California-Irvine and NASA's Jet Propulsion Laboratory.

"It really is an amazingly distressing situation," says Pennsylvania State University glaciologist Sridhar Anandakrishnan, who was not affiliated with either study. "This is a huge part of West Antarctica, and it seems to have been kicked over the edge."

The researchers say the fate of the glaciers is almost certainly beyond hope.

One study shows that a river of ice called Thwaites Glacier is probably in the early stages of collapse. Total collapse is almost inevitable, the study shows.

A second study shows that a half-dozen glaciers are pouring ice into the sea at an ever-greater pace. That will trigger 4 feet of sea-level rise, says study author Eric Rignot, a glaciologist at the University of California-Irvine, and NASA's Jet Propulsion Laboratory.

"The retreat of ice in that area is unstoppable," Rignot said at a briefing Monday, adding that the glaciers have "passed the point of no return."

Rignot and his team used data from satellites and aircraft to map changes in six West Antarctic glaciers and the terrain underlying these massive ice floes. The data show the glaciers are stretching out, thinning and shrinking in volume. They're also flowing faster from the continent's interior to the sea, dumping larger quantities of ice into the ocean than before and thereby raising sea levels.

At the same time, the portion of each glacier projecting into the sea is being melted from below by warm ocean water. That leads to a vicious cycle of more thinning and faster flow, and the local terrain offers no barrier to the glaciers' retreat, the researchers report in an upcoming issue of Geophysical Research Letters.

A report in this week's Science says the Thwaites Glacier will collapse, perhaps in 200 years. The paper doesn't specify the amount of sea-level rise associated with Thwaites' demise.